1. Field of the Invention
The present invention relates to an electric power steering system for a vehicle, and, more particularly, to a system for controlling a motor in accordance with the turning of a steering wheel.
2. Description of the Prior Art
Conventionally, in order to reduce the driver's steering effort, it is known for a vehicle to have an electric power steering system. For example, U.S. Pat. No. 4,664,211 discloses that an electric power steering system having a torsion torque sensor for measuring torsion torque in a steering shaft is adapted to control the rotational direction and torque of a motor depending on the output signal of the sensor.
In order to significantly reduce the consumption of battery power, control of the electric power steering system is carried out only when the engine is operated and an alternator is driven by the engine. Therefore, if engine stall occurs in the vehicle running condition, steering torque is rapidly increased. This rapid increment of the steering torque is not desirable for steering the vehicle.